I moved from a Mac to Linux some months ago but hadn't opened Simplify3D yet. I opened Simplify3D (4.1.1) and imported my .fff profile previously exported from the Mac. I then imported a model, edited the process settings accordingly, and tried to slice ("Prepare to Print!"). I got a message in the message area at the bottom of the window: "Failed to create final toolpaths".

OK, after a bit of quality time with strace I found that I had a permissions error. $HOME/.local/share/Simplify3D was owned by root (so it seems that at some point I did start it up with sudo). I was having another problem with S3D not saving my settings between sessions, and it was also a permissions problem, this time in $HOME/.config/Simplify3D (adding this one for future Googlers)